One environment in which increasing sealing problems have been encountered is in the sealing of valve covers to engine heads. Valve covers have been made of lighter weight materials, such as of aluminum and even of plastic, both of which tend to distort and deflect. Further, the heads are less dimensionally stable, compounding the difficulty of sealing.
Previously multilayer valve cover gaskets have employed combinations of a perforated metallic core and cork-rubber layers, even cork-rubber layers of different thicknesses, to attempt to provide an effective valve cover seal. However, it has been found that the perforated core, with the formed tangs, tends to rupture the associated cork-rubber layers, thereby destroying the impervious, sealing characteristics of the gasket. When conventional rubber-fiber or rubber-asbestos sheets were substituted for the cork-rubber layers it was found that they were ineffective to produce an adequately conforming gasket, hence were ineffective to produce a gasket which sealed effectively and properly.